1. Field of the Invention
The present invention relates to plasma-resistant articles that exhibit improved plasma-resistance in a corrosive atmosphere of halogen gas. The present invention further relates to a method for producing such an article.
2. Description of the Related Art
Apparatuses for etching microscopic features onto a semiconductor wafer are used, for example, in the production process of semiconductor devices, as are sputtering apparatuses and CVD apparatuses for depositing film on a semiconductor wafer. These types of manufacturing apparatuses generally employ a plasma generator for the microscopic scale-processing required to make highly integrated devices. For example, helicon wave plasma etchers such as the one shown schematically in cross-section in the accompanying drawing are known.
In the drawing, reference numeral 1 denotes an etch-process chamber, which includes an etching gas inlet 2 and a vacuum exhaust port 3. Circumferentially arranged about the process chamber 1 are an antenna 4, an electromagnet 5, and a permanent magnet 6. A lower electrode 8 is arranged inside the process chamber 1 to hold a semiconductor wafer 7 serving as a workpiece. The antenna 4 is connected to a first RF power source 10 via a first matching network 9 while the lower electrode 8 is connected to a second RF power source 12 via a second matching network 11.
This etching apparatus operates in the following manner. First, the etch-process chamber 1 is evacuated to vacuum with the semiconductor wafer 7 placed on the lower electrode 8. Etching gas is then supplied through the etching gas inlet 2. Subsequently, an RF current with a frequency of for example 13.56 MHz is allowed to flow from the RF power sources 10 and 12 through the respective matching networks 9 and 11 to the antenna 4 and the lower electrode 8, respectively. In the meantime, a predetermined current is allowed to flow through the electromagnet 5 to generate a magnetic field and thus high-density plasma in the process chamber 1. The energy of the plasma is then utilized to cause the etching gas to dissociate into atoms, which in turn are used to etch film deposited on a surface of the semiconductor wafer 8.
Apparatuses of this type make use, as the etching gas, of chlorine-based gases, such as carbon tetrachloride (CCl4) and boron chloride (BCl3), as well as of fluorine-based gases, such as fluorocarbons (e.g., CF4 and C4F8), nitrogen fluoride (NF3) and sulfur fluoride (SF6), each of which is known to be a corrosive gas. Thus, structural members, including inner walls of the process chamber 1, monitor windows, windows for introducing microwave, the lower electrode 8 and susceptors, that are to be exposed to plasma in an atmosphere of the corrosive gas must have an adequate plasma-resistance. To meet this requirement, materials such as alumina ceramics, sapphire, silicon nitride ceramics and aluminum nitride ceramics are used in the plasma-resistant members.
However, such plasma-resistant members, made from the aforementioned materials including alumina ceramics, sapphire, silicon nitride ceramics, and aluminum nitride ceramics, gradually corrode when exposed to plasma in a corrosive atmosphere. As a result, crystal particles forming surfaces may fall off the surfaces and the materials may react with fluorine to form aluminum fluoride, giving rise to the problem of particle contamination. The particles that have come off the surfaces attach to the semiconductor wafer 7, the lower electrode 8, and/or the adjacent area of the lower electrode 8 so as to adversely affect the precision of the etching process. As a result, the performance of the semiconductor is lowered, as is its reliability.
Corrosion-resistance is also required for CVD apparatuses, which are to be exposed to nitrogen fluoride and other fluorine-based gases in the presence of plasma during cleaning of the apparatus.
To provide the required degree of corrosion-resistance, plasma-resistant articles have been proposed that are made from an yttrium aluminate garnet (generally known as YAG) ceramic (examples are described in Japanese Patent Laid-Open publications No. Hei 10-45461 and No. Hei 10-236871). Despite their relatively high plasma-resistance as compared to alumina, use of the yttrium aluminate garnet-based ceramics tends to result in low yields when it is desired to apply microetching as in the case of forming microscopic circuit patterns. Furthermore, use of these materials adds to cost. For these reasons, a demand exists for cost effective materials that have high plasma resistance.
Stabilized zirconia ceramics that abundantly contain yttria have attracted attention in terms of cost reduction. That is, not only do the yttria-stabilized zirconia-based ceramics exhibit a plasma resistance 5 times or higher than that of alumina, but they also are less expensive than the yttrium alminate garnet ceramics and are thus expected to be advantageous in cost reduction.
The walls of the etch process chamber 1 are typically made of materials such as alumina ceramics, alumite and aluminum, so that aluminum fluoride by-products are formed during the plasma etching process involving the use of halogen gases and are deposited on the surfaces of structural members within the chamber, forming a layer there. Such a layer of aluminum fluoride may come off the surfaces to provide a source of dust. For this reason, not to mention the high plasma resistance, the structural members within the chamber must have the ability to suppress or prevent peeling of the dust-causing aluminum fluoride deposits.
To this end, surfaces of the plasma-resistant ceramics formed of yttria-stabilized zirconia-based materials are sandblasted to impart a roughness to prevent the aluminum fluoride deposits from coming off. However, treating the surfaces using the sandblast technique to impart surface roughness can damage the treated surfaces due to formation of microcracks and contamination of ceramic surfaces. Thus, this approach is not effective in preventing dust formation and contamination of the semiconductor devices.